Gas ionizers are used in various analytical instruments such as mass spectrometers and ion beam microscopes. Additionally, field ion sources are employed in portable neutron generators for oil well logging and detection of shielded nuclear materials. Traditionally, gas ionizers generate ions by electron impact ionization, where high-energy electrons collide with neutral molecules to create ions by fragmentation. Currently, state-of-the-art gas ionizers utilize either thermionic cathodes or field emission cathodes as electron source for electron impact ionization. In thermionic emission, electrons are excited to vacuum level using thermal energy, and in field emission, electrons are extracted from the emitter in a field-assisted tunneling process. Therefore, thermionic cathodes may consume more power and have slower response times than field emission cathodes, although field emission cathodes may require higher voltages to operate than thermionic electron sources.